EP1930177B1 - Projection blackboard and process for producing the same - Google Patents

Projection blackboard and process for producing the same Download PDF

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Publication number
EP1930177B1
EP1930177B1 EP05809636.3A EP05809636A EP1930177B1 EP 1930177 B1 EP1930177 B1 EP 1930177B1 EP 05809636 A EP05809636 A EP 05809636A EP 1930177 B1 EP1930177 B1 EP 1930177B1
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EP
European Patent Office
Prior art keywords
glaze
enamel layer
titanium dioxide
chalkboard
projection
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Application number
EP05809636.3A
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German (de)
English (en)
French (fr)
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EP1930177A1 (en
EP1930177A4 (en
Inventor
Kazuhiro Hayashi
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JFE Metal Products and Engineering Inc
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JFE Metal Products and Engineering Inc
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
    • B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
    • B05D3/0209—Multistage baking
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B43—WRITING OR DRAWING IMPLEMENTS; BUREAU ACCESSORIES
    • B43L—ARTICLES FOR WRITING OR DRAWING UPON; WRITING OR DRAWING AIDS; ACCESSORIES FOR WRITING OR DRAWING
    • B43L1/00—Repeatedly-usable boards or tablets for writing or drawing
    • B43L1/04—Blackboards
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B43—WRITING OR DRAWING IMPLEMENTS; BUREAU ACCESSORIES
    • B43L—ARTICLES FOR WRITING OR DRAWING UPON; WRITING OR DRAWING AIDS; ACCESSORIES FOR WRITING OR DRAWING
    • B43L1/00—Repeatedly-usable boards or tablets for writing or drawing
    • B43L1/04—Blackboards
    • B43L1/10—Writing surfaces thereof
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
    • G03B21/00—Projectors or projection-type viewers; Accessories therefor
    • G03B21/54—Accessories
    • G03B21/56—Projection screens
    • G03B21/60—Projection screens characterised by the nature of the surface
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
    • Y10T428/12611—Oxide-containing component
    • Y10T428/12618—Plural oxides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12993—Surface feature [e.g., rough, mirror]

Definitions

  • the present invention relates to a chalkboard (also referred as blackboard) having an enamel layer on its surface, in particular, an enamel chalkboard having both of an excellent chalkboard function and an excellent screen function.
  • excellent chalkboard function means that a chalkboard has a function that characters, pictures or the like are easily written/drawn thereon with a chalk and are easily watched, and the written/drawn characters, pictures or the like thereon are easily erased.
  • excellent screen function means that a chalkboard has a function that when images of characters or the like are projected thereon through a projector, an OHP or the like, the images of the characters or the like can be clearly projected.
  • chalkboards blackboards
  • JIS S 6007 the surface thereof has appropriately roughness in order that characters, pictures or the like can easily be written/drawn with a chalk or can easily be erased, and further dark color material has been used for the surface thereof in order that the written/drawn characters, pictures or the like can easily be watched.
  • JP-U Japanese Utility Model Application Laid-Open
  • JP-U Japanese Utility Model Application Laid-Open
  • No. 57-183190 suggests an enamel chalkboard which is also used as a projecting screen, having a rough-surface enamel layer on its surface which informed on a steel sheet using a glaze containing a blue dye and have a brightness of 4 to 8 on a steel sheet.
  • WO 02/37409 A1 discloses a method for manufacturing a writing board, according to which at least one electrically insulating enamel layer, at least one layer containing an emission or reception part of an electronic position detection device, and at least one porcelain enamel finishing layer are provided on a substrate comprising a plate of enamellable metal.
  • the electrically insulating enamel layer, the finishing enamel layer and said at least one layer containing the emission or reception part are made from firable compositions which are subjected to a firing.
  • DE 27 49 402 A1 discloses a method for manufacturing a writing board having an enamel-type resin coating, comprising the steps of mixing anhydrous borax, at least two alkali metal compounds, and a suitable pigment such as, for example, titanium dioxide to form a mixture, repeatedly heating and cooling the resulting mixture until a frit is formed, mixing the resulting frit with a heat-curable resin to form a composition, and applying the resulting composition to a board and compressing it, to thereby form the writing board.
  • a suitable pigment such as, for example, titanium dioxide
  • the chalkboard produced by the technique described in Japanese Utility Model Application Laid-Open (JP-U) No. 57-183190 has low reflective luminance and shows a tendency to give an unclear image.
  • JP-U Japanese Utility Model Application Laid-Open
  • a clear image can hardly be obtained on that black board. In such a way, there remain problems that the chalkboard cannot satisfy recent properties required for a screen sufficiently.
  • An object of the present invention is to solve the above-stated problems in the prior art favorably and provide a projection chalkboard having both of an excellent chalkboard function and an excellent screen function, on which characters, pictures or the like are easily written/drawn with a chalk and are easily watched so as to give an excellent chalk-character-recognizable property, on which characters, pictures or the like written/drawn with a chalk can easily be erased to give an excellent chalk-character-writable/drawable/erasable property besides an excellent chalk-character-recognizable property, and on which projected images can be clearly screened to give an excellent projected-image-recognizable property; and a producing process thereof.
  • the projection chalkboard which is a target of the present invention is an enamel chalkboard having one or more enamel layers on an outer surface of a metallic substrate.
  • the inventors have made eager investigations on factors producing effects onto the chalk-character-recognizable property, the chalk-writable/drawable/erasable property, and the projected-image-recognizable property of an enamel chalkboard.
  • the inventors have found out that it is important to prepare a surface enamel layer of a chalkboard in such a manner that: the surface enamel layer has a brightness in a predetermined range and a surface roughness in a predetermined range to keep certainly chalk-character-recognizable property, chalk-character-writable/drawable/erasable property which are equal to or more than those of conventional chalkboards; and further the layer has such a reflective property that the layer has a peak gain not lower than a predetermined value in order to improve the projected-image-recognizable property.
  • Such a surface enamel layer can be produced by using a glaze to be used a glaze wherein at least an appropriate amount of titanium dioxide coated particles, or a titanium dioxide glaze together therewith is blended into a transparent mat glaze, which is an ordinary chalk board glaze, and by adjusting the firing conditions into an appropriate range. It has been found out that this manner makes it possible to cause a chalkboard to have both of an excellent chalkboard function and an excellent screen function.
  • the projection chalkboard according to the present invention is a chalkboard having one or more enamel layers on a metallic substrate.
  • the kind of the used metallic substrate is not particularly limited.
  • the substrate is preferably a cold-rolled steel sheet. It is preferred to plate the cold-rolled steel sheet used as the metallic substrate with Ni in order to improve the adhesive property of the metallic substrate to a glaze.
  • the cold-rolled steel sheet include a low-carbon steel sheet and a stainless steel sheet.
  • the C content in the low-carbon steel sheet is preferably 0.0200% or less by mass, more preferably 0.0100% or less by mass, even more preferably 0.0050% or less by mass.
  • the metallic substrate may be an aluminum plated steel sheet or a Zn-Al alloy plated steel sheet.
  • Zn-Al alloy plated steel sheet include a plated steel sheet having a plating layer consisted of 4 to 70% by mass ofAl and the balance made of Zn and inevitable impurities. It is needless to say that an additive for improving a property of the plated coat may be included into the plating layer.
  • the surface enamel layer that is an outermost layer out of the enamel layers formed on the metallic substrate has a color tone that the brightness V prescribed in JIS Z 8721-1993 is from 4.0 to 6.0, a surface characteristic that the surface roughness Rz prescribed in JIS B 0601-2001 is from 5 to 25 ⁇ m, a reflective characteristic that the peak gain is from 0.5 to 1.0, and a surface gloss so that the 75-degree mirror plane glossiness Gs (75°) prescribed in JIS Z 8741-1997 is from of 15 to 25%.
  • the brightness V referred to in the present invention is a value measured in accordance with a color-measuring method prescribed in JIS Z 8722-2000 and represented by a color-representing method prescribed in JIS Z 8721-1993.
  • the projection chalkboard of the present invention is first required to have a chalk-character-recognizable property and chalk-character-erasable property which are equal to or more than those of conventional chalkboards, so as to keep an excellent chalkboard function.
  • the surface enamel layer is first rendered a surface enamel layer having a color tone that the brightness V prescribed in JIS Z 8721-1993 is from 4.0 to 6.0 and the layer is preferably in any one of black, green, brown and dark blue, more preferably in a dark color selected from black, green or brown. If the brightness V falls down from the above-mentioned range, the chalkboard becomes too dark so that the projected-image-recognizable property deteriorates when images are projected thereon. On the other hand, if the brightness V rises up from the range, the chalkboard becomes too bright so that the chalk-character-recognizable property deteriorates.
  • the color tone and the brightness of the enamel layer can be adjusted by the kind of the pigment(s) to be added, or the added amount thereof.
  • the surface characteristic of the surface enamel layer is adjusted in such a manner that the surface roughness Rz prescribed in JIS B 0601-2001 is turned into the range of 5 to 25 ⁇ m in order to keep certainly a chalk-character-writable/drawable/erasable property, which is a property that characters, pictures or the like are easily written/drawn with a chalk and are easily erased.
  • the surface roughness is preferably from 10 to 22 ⁇ m, more preferably from 14 to 18 ⁇ m.
  • the surface property of the above-mentioned surface enamel layer can be attained by setting a combination of the composition of the glaze to be coated on the metallic substrate and the firing conditions after the glaze is coated into an appropriate range.
  • the surface enamel layer has the above-mentioned color tone and surface characteristic to maintain an excellent chalkboard function, and further has a reflective characteristic that the peak gain is from 0.5 to 1.0, and preferably the half gain is 15 or more.
  • the reflective characteristic of a sheet to be measured is obtained from a reflective characteristic curve (see Fig. 1 ) gained as follows: incident light 1 is radiated from a light source 10 perpendicularly to the center of a plate 3s to be measured; and a luminance meter 11 is used to measure the intensity of reflected light 2 (reflective luminance) at each of points shifted right-handedly and left-handedly in the range of 75°, respectively, from the central point at intervals of 5° on the arc of a single circle.
  • the “peak gain” referred to in the present invention means the ratio of the reflective luminance of a chalkboard to be measured which is measured when light is radiated onto the chalkboard to that of a standard whiteboard (perfect diffusion plate: a purely white plate, on which barium sulfate is baked) measured under the same conditions.
  • the reflective luminance at a viewing angle of 5° is usually used.
  • the "half gain” referred to in the present invention means the viewing angle width (degree(s)) when the reflective luminance becomes 1/2 of that at the peak in the reflective characteristic curve.
  • the lower limit of the peak gain is set to 0.5 and the peak gain is from 0.5 to 1.0.
  • the half gain is preferably set to 15 or more.
  • the surface enamel layer is rendered a surface enamel layer having a reflective characteristic of which has a peak gain of from 0.5 to 1.0 and preferably a half gain of 15 or more.
  • the above-mentioned reflective characteristic of the surface enamel layer can be attained by: adding, to a glaze to be coated onto the metallic substrate, an appropriate amount of mica particles coated with titanium dioxide, having an appropriate particle diameter distribution; and adjusting the firing temperature into an appropriate range.
  • the surface enamel layer having the above-mentioned characteristics has such a surface gloss that the 75-degree mirror plane glossiness Gs (75°) is from 15 to 25%, the Gs (75°) being prescribed in JIS Z 8741-1997. If the Gs (75°) is less than 1%, the chalk-character-erasable property deteriorates and further the reflective luminance becomes small so that projected images get unclear. On the other hand, if the Gs (75°) is more than 30%, the chalk-character-writable/drawable property deteriorates and further halation is easily caused to make the viewing angle narrow.
  • the surface enamel layer contains titanium dioxide coated particles.
  • the containing of the titanium dioxide coated particles into the surface enamel layer causes an improvement in the clearness, and causes the formation of irregularities on the surface to improve the diffusion reflectivity. Thus, halation is restrained so as to improve the reflective characteristic.
  • the titanium dioxide coated particles are contained in the surface enamel layer in an amount of 2 to 40% by mass of the whole of the surface enamel layer, more preferably in an amount of 3 to 20% by mass thereof. If the amount of the titanium dioxide coated particles is less than 2% by mass, the reflective characteristic improving effect is small. If the amount of the titanium dioxide coated particles is more than 40% by mass, the surface roughness Rz becomes excessively large so that the chalk-character-erasable property deteriorates. Additionally, the brightness becomes too large so that the chalk-character-recognizable property decreases.
  • the titanium dioxide coated particles have an average particle diameter of 5 to 80 ⁇ m. If the average particle diameter of the titanium dioxide coated particles is less than 5 ⁇ m, the diffusion reflectivity falls. On the other hand, if the average particle diameter of the titanium dioxide coated particles is more than 100 ⁇ m, the surface roughness of the surface enamel layer becomes excessively large so that the chalk-character-erasable property decreases.
  • the average particle diameter of the particles referred to herein means the 50% cumulated particle diameter measured by use of a laser diffraction type particle size distribution measuring device.
  • the titanium dioxide coated particles are particles wherein surfaces of mica particles are coated with titanium dioxide.
  • the mica particles are preferably thin-plate-form mica particles.
  • the surface enamel layer having the above-mentioned properties isan enamel layer formed by using an enameling upper glaze obtained by blending, into a transparent mat glaze, at least titanium dioxide coated particles, optionally a titanium dioxide glaze together therewith, or a transparent gloss glaze together with the two.
  • the thickness of the surface enamel layer is preferably 200 ⁇ m or less from the viewpoint of the peel property thereof. The thickness is more preferably 150 ⁇ m or less.
  • the surface enamel layer formed by using the enameling upper glaze stated above is preferably a enamel layer containing: TiO 2 , which is total amount of titanium dioxide including titanium dioxide in the titanium dioxide coated particles: 0.5 to 15% by mass, more preferably 0.5 to less than 10% by mass, more preferably 2 to 5% by mass; SiO 2 : 15 to 45%; Al 2 O 3 : 5 to 30%; the total of one or more selected from Na 2 O, K 2 O and Li 2 O: 2 to 20% by mass; and B 2 O 3 : 2 to 20% by mass.
  • the enamel layer of the chalkboard contains one or more pigments selected from black pigments, green pigments, and yellow pigments in a total amount of 20% or less by mass in order to give a desired color.
  • the projection chalkboard of the invention is preferably produced by a producing process wherein: an enameling lower glaze is coated onto a surface of a metallic substrate and the resultant is fired to form an underlying enamel layer, or no underlying enamel layer is formed; an enameling upper glaze in which at least titanium dioxide coated particles, optionally a titanium dioxide glaze together therewith, or a transparent gloss glaze together with the two is blended into a transparent mat glaze is then coated thereon; and the resultant is fired at 400 to 850°C to form a surface enamel layer.
  • the metallic substrate is preferably a cold-rolled steel sheet, an aluminum plated steel sheet, or a Zn-Al plated steel sheet.
  • the cold-rolled steel sheet When a cold-rolled steel sheet is used as the metallic substrate, it is preferred to plate the cold-rolled steel sheet with Ni, coat an enameling lower glaze on a surface of the cold-rolled steel sheet (the metallic substrate), and fire the resultant to form an underlying enamel layer.
  • the enameling lower glaze is not particularly limited, and is preferably any enameling lower glaze that is used in conventional enamel chalkboards.
  • any known coating manner may be used, example thereof including spray and a roll coater.
  • the enameling lower glaze is preferably, for example, a SiO 2 based glaze comprising SiO 2 : 20-80%, and the balance composed of TiO 2 : 0-15%, ZrO 2 : 0-20%, B 2 O 3 ..
  • An enameling upper glaze is coated on the surface of the resultant underlying enamel layer, and subsequently the resultant is fired at 600 to 850°C to form a surface enamel layer.
  • any known coating manner may be used, example thereof including spray and a roll coater.
  • the enameling upper glaze is preferably a glaze wherein an appropriate amount of titanium dioxide coated particles are added to a transparent mat glaze (frit) or to a glaze wherein 100 to 20 parts by weight of a titanium dioxide glaze (frit) or 20 parts or less by weight of a transparent gloss glaze (frit) together therewith is added to 100 parts by weight of a transparent mat glaze (frit).
  • the added amount of the titanium dioxide coated particles is preferably from 1 to 25 parts by weight for 100 parts by weight (a value converted to weight after the firing) of the transparent mat glaze or the mixed glaze (slip).
  • the enameling upper glaze is obtained by adding/mixing an appropriate amount of powder of titanium dioxide coated particles to/with a slip obtained by grinding a mixture of: a frit of a transparent mat glaze, or a transparent mat glaze, a titanium dioxide glaze, or further a frit of a transparent gloss glaze; optional various additives and one or more optional pigments; and water. It is necessary to add any one of black pigment, green pigment, and yellow pigment or a combination of two or more thereof, as the pigment(s), in accordance with a desired color tone of the chalkboard.
  • the total added amount of the pigment(s) is preferably 20 parts or less by weight for 100 parts by weight (a value converted to weight after the firing) of the slip. If the added amount is more than 20 parts by weight so that the amount of the pigment(s) becomes large, the fluidity of the slip decreases.
  • the transparent mat glaze is preferably a glaze comprising SiO 2 : 30-45%, Al 2 O 3 : 20-35%, B 2 O 3 : 5-15%, K 2 O: 5-15%, Na 2 O: 10-25%, and the balance composed of BaO: 0-15%, CaO: 0-15%, F 2 : 0-10%, TiO 2 : 0-10%, and so on, each "%" representing % by mass relative to the basis of the whole of solid contents therein.
  • the titanium dioxide glaze is preferably a glaze comprising 10 to 30 % of TiO 2 and the balance composed of SiO 2 : 0-80%, Al 2 O 3 : 0-20%, B 2 O 3 : 0-25%, Na 2 O: 0-20%, K 2 O: 0-20%, Li 2 O: 0-20%, P 2 O 5 : 0-10%, ZrO 2 : 0-20%, BaO: 0-15%, CaO: 0-15%, MgO: 0-5%, PbO: 0-40%, ZnO: 0-50%, CaF 2 : 0-10%, and so on, each "%" representing % by mass relative to the basis of the whole of solid contents therein.
  • titanium dioxide which is a pigment of the titanium dioxide glaze
  • one or more pigments out of zirconium oxide, antimony oxide and zinc oxide may be used.
  • the transparent gloss glaze is preferably a glaze comprising SiO 2 : 40-65%, and the balance composed of B 2 O 3 : 5-20%, one or more out of Na 2 O, K 2 O and Li 2 O : 5-40% in total, F 2 : 0-10%, Al 2 O 3 : 0-10%, CaO: 0-10%, TiO 2 : 0-10%, ZnO: 0-10%, MgO: 0-5%, and so on, each "%" representing % by mass relative to the basis of the whole of solid contents therein.
  • titanium dioxide which is a pigment of the titanium dioxide glaze
  • one or more pigments out of zirconium oxide, antimony oxide and zinc oxide may be used.
  • the firing temperature is lower than 600°C, the surface roughness becomes too rough so that the reflective characteristic deteriorates.
  • the temperature is higher than 850°C, the surface becomes too flat and smooth so that the chalk-character-recognizable property and the chalk-character-writable/drawable/erasable property decline.
  • an aluminum plated steel sheet or a Zn-Al alloy plated steel sheet it is preferred to coat an enameling upper glaze onto a surface of the metallic substrate and fire the resultant at 400 to 600°C to form a surface enamel layer.
  • an enameling upper glaze having a low melting point it is necessary to use an enameling upper glaze having a low melting point to prevent the plating layer from being melted. It is therefore preferred to use an enameling upper glaze wherein titanium dioxide coated particles or a titanium dioxide glaze together therewith is blended into a glaze wherein phosphoric acid is blended instead of the above-mentioned transparent mat glaze.
  • the phosphoric acid content by percentage in the glaze into which phosphoric acid is blended is 40% or more by mass and is preferably 80% or less by mass, more preferably 70% or less by mass.
  • the glaze (frit) into which phosphoric acid is blended is preferably a glaze comprising P 2 O 5 : 40-80%, and the balance composed of SiO 2 : 0-40%, Al 2 O 3 : 0-50%, B 2 O 3 : 0-25%, Na 2 O: 0-20%, K 2 O: 0-20%, Li 2 O:0-20%, TiO 2 : 0-30%, Sb 2 O 3 :0-25%, ZnO: 0-20%, BaO: 0-15%, CaO: 0-15%, MgO: 0-5%, PbO: 0-10%, SrO: 0-20%, and so on, each "%" representing % by mass relative to the basis of the whole of solid contents therein.
  • an enameling upper glaze having a low melting point is used to prevent the plating layer from being melted; thus, the adhesiveness is improved so that it is not necessarily essential to coat the enameling lower glaze.
  • the adhesiveness of the enamel layer decreases if the firing temperature is lower than 400 °C. On the other hand, if the temperature is higher than 600 °C, a problem that the plating layer is melted is caused. Examples
  • a cold-rolled steel sheet (an extremely low carbon steel sheet containing C: 0.0050% by mass) was used as each metallic substrate.
  • a nickel plating layer was formed on each surface of the cold-rolled steel sheet in a nickel sulfate bath.
  • an enameling lower glaze was coated onto each surface of the cold-rolled steel sheet, which was plated with the nickel, in a roll coater manner. Thereafter, the resultant was fired at 800°C to form an underlying enamel layer 30 ⁇ m in thickness.
  • the used enameling lower glaze was a glaze obtained by charging, into a ball mill, a blend material wherein clay: 6 parts by weight, magnesium carbonate: 0.15 part by weight, borax: 0.4 part by weight, silica: 1 part by weight, and water: 70 parts by weight were added to a SiO 2 based glaze (frit): 100 parts by weight, and then mixing/grinding the components into a slip.
  • an enameling upper glaze was coated onto one of the surfaces of the resultant underlying enamel layer in a spraying manner. Thereafter, the resultant was fired at 750°C to form a surface enamel layer 70 ⁇ m in thickness. In such a way , sample chalkboards were produced. About some of the chalkboards, the firing temperature was varied in the range of 700 to 780°C.
  • a transparent mat glaze having a composition shown in Table 1 were added clay: 5.5 parts by weight, sodium nitrite: 0.15 part by weight, silica: 0.5 part by weight, and water: 70 parts by weight, and further to the mixture were added TiO 2 , Sb 2 O 5 and NiO: 1 part by weight in total, Cr 2 O 3 : 8.2 parts by weight, Co and Cr: 10.0 parts by weight in total, and Fe 2 O 3 , CuO, CoO, MnO and so on: 0.1 part by weight in total as pigments.
  • the components were mixed/grinded in a ball mill to yield a slip A.
  • a titanium dioxide glaze having a composition shown in Table 2 were added clay: 5.5 parts by weight, potassium chloride: 0.2 part by weight, sodium aluminate: 0.3 part by weight, and water: 54 parts by weight, and the components were mixed/grinded to yield a slip B. Thereafter, to the slip B: 100 parts by weight were added powder of titanium dioxide coated particle: 20 parts by weight (a value converted to weight after the firing) together with water: 45 parts by weight. The components were mixed to prepare a slip C. The slip A and the slip C were blended with each other at a ratio of 3 to 1 to prepare each enameling upper glaze which was used in the present invention. In some of the glazes, the mixing ratio between the slip A and the slip C was varied.
  • the titanium dioxide coated particle powder was made of particles wherein surfaces of thin-plate-form mica particle were coated with titanium dioxide, and had an average particle diameter of 20 ⁇ m and a titanium dioxide coated area ratio of 30%.
  • the average particle diameter was the 50% cumulated particle diameter measured by use of a laser diffraction type particle size distribution measuring device.
  • a transparent mat glaze having the composition shown in Table 1 were added clay: 5.5 parts by weight, sodium nitrite: 0.15 part by weight, silica: 0.5 part by weight, and water: 70 parts by weight, and further to the mixture were added TiO 2 , Sb 2 O 5 and NiO: 0.5 part by weight in total, Cr 2 O 3 : 4.1 parts by weight, Co and Cr: 5.0 parts by weight in total, and Fe 2 O 3 , CuO, CoO, MnO and so on: 0.05 part by weight in total as pigments.
  • the components were mixed/grinded in a ball mill to yield a slip D.
  • the slip D was used as an enameling upper glaze, and firing at a firing temperature of 700°C was carried out.
  • a contact type surface roughness meter was used to obtain the arithmetic average roughness Ra and the maximum height Rz in accordance with JIS B 0601-2001.
  • the color tone was measured in accordance with JIS Z 8722-2000, and the color tone of each of the sample chalkboards was represented in accordance with JIS Z 8721-1993.
  • the 75-degree mirror plane glossiness Gs (75°) was obtained in accordance with JIS Z 8741-1997.
  • incident light 1 was radiated from a light source 10 perpendicularly to the center of a plate 3s to be measured, and a luminance meter 11 was used to measure the intensity of reflected light 2 (reflective luminance) at each of points shifted right-handedly and left-handedly in the range of 75°, respectively, from the central point at intervals of 5° on the arc of a single circle.
  • the peak gain and the half gain were then obtained.
  • the peak gain the ratio of the reflective luminance of the sample chalkboard which was measured when light was radiated onto the chalkboard to that of a standard whiteboard (perfect diffusion plate: a purely white plate, on which barium sulfate was baked) measured under the same conditions.
  • the reflective luminance the reflective luminance at a viewing angle of 5° was used.
  • Fig. 1 Examples of the reflective characteristics of the chalkboards of the present invention (the present invention articles) and the conventional chalkboard (the conventional article) are shown in Fig. 1 .
  • the reflective luminance of the measured chalkboards is represented by the percentage when the reflective luminance of the standard luminance (the peak) is set to 100%.
  • the present invention examples each maintained a chalk-character-recognizable property and a chalk-character-erasable property equivalent to those of the conventional chalkboard to keep an excellent chalkboard function, and further gave a peak gain of from 0.5 to 1.0 to exhibit an excellent reflective characteristic.
  • the chalkboards are chalkboards excellent in projected-image-recognizable property and suitable for image-projection.
  • the comparative example outside the scope of the present invention had a lowered chalkboard function of chalk-character-recognizable property and chalk-character-erasable property, or had a poor reflective characteristic with declined the projected-image-recognizable property thereof.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Drawing Aids And Blackboards (AREA)
  • Overhead Projectors And Projection Screens (AREA)
EP05809636.3A 2005-09-02 2005-11-28 Projection blackboard and process for producing the same Active EP1930177B1 (en)

Applications Claiming Priority (2)

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JP2005254586 2005-09-02
PCT/JP2005/021772 WO2007029351A1 (ja) 2005-09-02 2005-11-28 映写黒板およびその製造方法

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EP1930177A4 EP1930177A4 (en) 2010-12-29
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EP (1) EP1930177B1 (zh)
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CN101870223A (zh) * 2009-04-21 2010-10-27 王志明 搪瓷面智能白板
BR112012019442A2 (pt) * 2010-01-26 2016-05-03 3M Innovative Properties Co artigo e método
CN102774181A (zh) * 2011-05-13 2012-11-14 张德林 搪瓷投影黑板
CN102689553A (zh) * 2012-05-29 2012-09-26 张秀英 一种电热橡皮擦
JP6302342B2 (ja) * 2014-04-24 2018-03-28 Ｊｆｅ建材株式会社 映像認識性に優れた暗線付き映写黒板
BE1021935B1 (nl) * 2014-06-03 2016-01-27 Polyvision Naamloze Vennootschap Projectie-en communicatiebord en werkwijze om het te vervaardigen
CN105955640A (zh) * 2016-05-22 2016-09-21 欧光君 一种交互式电子白板系统
CN111976344A (zh) * 2020-08-31 2020-11-24 福州神罗信息技术有限公司 可投影黑板及其制造设备
CN112573944B (zh) * 2020-12-14 2023-03-24 张万里 陶瓷基体激光电视显示屏及其制作方法

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US20130216715A1 (en) 2013-08-22
CN100591531C (zh) 2010-02-24
CN101258040A (zh) 2008-09-03
US9168566B2 (en) 2015-10-27
TWI359748B (zh) 2012-03-11
EP1930177A1 (en) 2008-06-11
TW200709956A (en) 2007-03-16
WO2007029351A1 (ja) 2007-03-15
EP1930177A4 (en) 2010-12-29
US8470451B2 (en) 2013-06-25
US20090155759A1 (en) 2009-06-18

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